Vol. 4] 



Knopf. — Foothill Copper Belt. 



413 



Clay and gouge are frequent, as on the other hand are lenses of 

 massive, unsheared rock in the midst of the schists. The ore 

 consists of chalcopyrite in a gangue of a spherulitic zeolite (Sp. 

 gr. 2.17) replacing a chlorite schist. The microscope shows radial 

 stilbite,* quartz charged with liquid inclusions, areas of chlorite, 

 often consisting of small partially developed spherulites, and 

 accessory epiclote and calcite. The most nearly massive wall rock 

 obtainable is composed largely of green, reedy hornblende, 

 chlorite, highly altered plagioclase, and accessory epidote, pyrite, 

 and magnetite. 



At Spenceville the ore body occurs in andesites whose extru- 

 sive character is readily apparent. Facies carrying numerous 

 quartz amygdules occur in the bed of Little Dry Creek, and the 

 cryptocrystalline facies on the brow of the hill just behind the 

 mine dump is rich in epidote amygdules. A few hundred feet 

 to the west, however, typical ophitic diabase occurs. This has 

 been cut by fine grained dykes of similar chemical composition. 

 The dykes show that minor faulting has taken place, not exceed- 

 ing half a foot in individual cases. Some two hundred feet east 

 of the Spenceville mine the greenstones are intruded by a large 

 granodiorite boss. Lindgren has characterized the Spenceville 

 deposit as a "local massing of copper on the granodiorite 

 contact. ' 't 



The mine has been a quite large producer in the past, but is 

 now idle and filled with water. From report it appears that the 

 ore body consisted of one huge kidney of chalcopyrite which 

 pinched out in depth. 



PINE HILL, NEVADA COUNTY. 



This locality has been described by Lindgren, who drew atten- 

 tion to the unusual fact that here barite acts as a carrier of gold. J 

 The deposit was characterized as of the general type; "veins and 



* The optical properties of this zeolite diverge from those of stilbite in 

 two important particulars ; it shows an absorption equal to that of nmseov- 

 ite, and displays brilliant interference colors of the 2nd and 3rd orders. 

 Otherwise the physical and chemical properties are identical with those of 

 stilbite. 



t Smartsville Folio. 



t W. Lindgren, The Gold Deposit at Pine Hill, California; A. J. S. 3rd 

 ser., vol. XLIV., pp. 92-96, 1892. 



